1. Field of the Invention
This invention relates to rust-proof lubricant compositions of the solid film type for use with metals which are applied on the surfaces of hot rolled steel plates, cold rolled steel plates and surface treated steel plates (hereinafter abbreviated as "steel plates") to effect temporary rust-proofness of the steel plates and/or an improvement in lubrication at the time of forming. More particularly, the present invention is directed to rust-proof lubricant compositions comprising partial esters of pentaerythritol with fatty acid, as the chief constituents, rust-preventitives, lubrication-improving agents, surface active agents, etc., having melting points of 30.degree.-60.degree. C., which can be applied on steel plates without the necessity of any solvent or heat-drying, and which may be adapted for the continuous coating of steel plates.
2. Description of the Prior Art
In general there are two types of compositions which are used to effect a temporary rust-prevention and/or forming lubrication of steel plates, one of which is the liquid film type, contains components capable of improving the rust-proof and lubrication added into a base oil, for example, mineral oil, animal oil, or vegetable oil, such as, metal working oil, anti-rusting oil, etc., and the other of which is of the solid film type and contains a fatty acid, or fatty acid soap as the main constituents.
In comparing both types, the liquid coating has the disadvantage that when the steel plates are fabricated by press forming, some of the coating drops onto the floor and a dangerous slipping hazard exists. Moreover, the environment is polluted by the bad odor and scattering of the liquid which soils the clothes of the operators. Also, the formability can not be kept constant because the coating can not be held for long periods in the quality or the quantity necessary for forming. On the other hand, the solid coating does not present such problems. But the known solid coating composition should be dissolved in hot water, or an organic solvent before use, and the steel plates coated with the solution should be heated to dryness to remove the water or the solvent.
On one hand, the solid coating has a better effect on the stamping than the liquid coating as mentioned above. But, on the other hand, the coating process prior to the forming is more complicated, and requires facilities for coating and for drying by heating. Further, the heating lowers the quality of the steel sheet itself due to the strain ageing effect, so that it is not common to apply the solid coating in place of the liquid coating.
However, with the steel plate makers manufacture steel plates coated with rust-proof lubricant compositions of the solid film-type, users can directly place the coated steel plate into the forming operation without encountering the above-mentioned problems so that improvements in the operating conditions and productivity to counterbalance the additional costs will be easily achieved.
The rust-proof lubricants of the solid film-type are classified as of the solvent-type, aqueous solution-type, and reaction-type.
As for the solvent-type, the principal constituents, such as, fatty acid, extreme pressure additives, rust-preventives, etc., should be dissolved in an organic solvent before applying it on steel plates. In the case of the aqueous solution type, the principal constituents which are metal soaps of fatty acid and certain water-soluble organic compounds and inorganic compounds should be dissolved in hot water, and the coating applied on metal plates is dried by heating to form the solid film. In the reaction type, there is a lubricant comprising a phosphate-fatty acid soap. However, these conventional rust-proof lubricant compositions of the solid film type have many disadvantages, e.g.:
(1) The solvent-type uses an organic solvent so that when a large amount of the composition is used, for example, in the process for coating coils of steel sheets continuously, there arise the dangers from fire and explosion, sanitary problems, and special facilities are thus made necessary. Even if a highly noncombustible solvent is used, operators will not be free from the sanitary problems, such as, bad odor, poisoning by solvent, etc. Further, the waste gases produced when drying presents pollution problems. Additional problems include difficulty in degreasing in a short period of time in the surface-treating step after the forming operation.
(2) The aqueous solution type does not have the above-mentioned dangers from fire, or poisoning by solvent, because of the use of water, but high temperatures and long periods of time are necessary for drying, so that it is not only difficult to apply at a high speed on coils of steel plates, but also it is unsuitable to use for aging steel plates of which the mechanical properties are lowered by heating. Furthermore, since there is a close relationship between the melting point of compositions of the solid film-type and the pressing formability, the conventional water-soluble solid coatings are, in most cases, composed of compounds having high melting points, such as, fatty acid soaps and do not melt at the time of stamping. In drawing process, coating film is rubbed off with die surface and especially by die throat, and then splits of the coating film pile on die surface which hinders the steel plates from sliding into the dies. Further, the film does not have the fluidity to cover again the naked surface rubbed off by the drawing in larger sizes, therefore, cause pressing damages or reduce the pressing formability.
(3) The reaction-type complicates both the coating treatment and the subsequent removal treatment.
As has been mentioned above, while the conventional rust-proof lubricants of the solid film-type have many defects, the present invention overcomes all of these defects and provides compositions having very important properties.